1. Field of the Invention
The present invention relates to a gas-insulated switchgear apparatus and a gas filter device for the gas-insulated switchgear apparatus.
2. Description of the Related Art
Japanese Patent Application Laid-open No. H5-91631 discloses a technique of filling an insulating gas in a gas-insulated switchgear apparatus. The conventional gas-insulated switchgear apparatus includes a plurality of metallic chambers, each of which is partitioned by an insulating spacer and hermetically filled with an insulating gas. A gas valve is arranged at a gas filling opening of each metallic gas chamber. The gas valve is opened at the time of filling or evacuating an insulating gas. That is, the gas valve is opened when the gas-insulated switchgear apparatus is connected to a gas filling apparatus or a gas evacuating apparatus through a gas pipe.
Moreover, the gas-insulated switchgear apparatus includes a bypass piping for performing central monitoring of the gas pressure in metallic chambers. The bypass piping has a valve arranged between each pair of two neighboring metallic chambers. Each valve is usually kept open during the central monitoring but is closed when the gas pressure in each metallic gas chamber is to be monitored individually.
However, when the gas valve is opened to fill an insulating gas in the abovementioned gas-insulated switchgear apparatus, there is a possibility that foreign objects of equal to or larger than about three millimeters in length enter therein from the gas filling opening. Such foreign objects affect the insulating properties of the gas-insulated switchgear apparatus and may cause an insulation breakdown.
To avoid such a problem, some conventional gas-insulated switchgear apparatuses are equipped with a gas filter device for filtering an insulating gas being filled. However, a gas filter device may not prevent all foreign objects accumulated in a gas pipe, which connects a gas-insulated switchgear apparatus and a gas filling apparatus, from entering into in the gas-insulated switchgear apparatus.
Moreover, if, e.g., a grounding fault occurs in one of the metallic chambers, there is a possibility that foreign objects, decomposition product, or a cracked gas generated in the faulty metallic gas chamber flows into a neighboring metallic gas chamber through the bypass piping. That is because the valves in the bypass piping are usually kept open. As a result, it becomes necessary to carry out the appropriate gas treatment in all the contaminated metallic chambers.